Tip

Buying smoked haddock
This is my favourite fish – you can’t find it anywhere else in the world and, as a flavour, it makes a dish feel inherently British. For the best smoked haddock, look for cold-smoked fish from Grimsby or Scotland that is undyed – this means it will be pale rather than a bright yellow. If you can only find yellow smoked haddock, try to buy fish that has been naturally dyed using turmeric. A good-quality piece of smoked haddock will have a dry appearance and the flesh will have a shine. Smoked haddock will keep for longer than fresh fish, so you can buy it a few days before, if that helps you to get ahead.

Method

Bring the milk, bay and peppercorns to a simmer in a large shallow pan. Drop in the haddock, turn off the heat, cover with a lid or foil and leave to cool for 30 mins – the haddock will be just cooked. Carefully remove the haddock and set aside on a plate, then strain the milk through a sieve into a jug. To prepare the haddock, remove the flesh from the skin, making sure all bones and spices have been discarded – the fish should break into natural bite-sized flakes. Set aside until needed.

Heat the oil and a small knob of butter in a pan. Add the onion and garlic and cook until softened, about 15 mins. Add the leeks and continue cooking for 2 mins. Drain in a colander and leave to cool.

In the same pan, melt the 75g butter, then stir in the flour to form a paste. Cook for 3-4 mins without colouring, then slowly ladle in the warm milk, stirring constantly with a wooden spoon, until you have a glossy sauce. Stir in the mustard poweder, lemon juice and some seasoning, then pass through a fine sieve.

Heat oven to 180C/160C fan/gas 4. To assemble the pie, place the leeks in the bottom of a 1.6-litre pie dish (about 22cm) and top with a third of the sauce. Follow with the flaked smoked haddock and another third of the sauce. Finally, scatter over the cheese and top with the remaining sauce, making sure the filling is completely covered.

For the filo crust, melt the butter in a small pan, then add the garlic. Heat gently for 5 mins to allow the garlic to infuse. Lay one sheet of filo on a chopping board and brush all over with the garlic butter, then sprinkle with some chives and cracked black pepper. Place another sheet of pastry on top at a slight angle and repeat. Continue in this way until you have used up all the pastry and almost all the garlic butter. You should have created a jagged-edged pastry circle. Lay this on top of the pie dish, then use a sharp knife to trim the edges, but still leave an overhang. Brush with a final layer of butter, sprinkle with flaky sea salt and bake for 40 mins or until the pastry is golden and crisp. Serve with the Charred Baby Gem, watercress & bacon salad (see recipe, Goes well with).